[ValueTracking] Introduce a KnownBits struct to wrap the two APInts for computeKnownBits

This patch introduces a new KnownBits struct that wraps the two APInt used by computeKnownBits. This allows us to treat them as more of a unit.

Initially I've just altered the signatures of computeKnownBits and InstCombine's simplifyDemandedBits to pass a KnownBits reference instead of two separate APInt references. I'll do similar to the SelectionDAG version of computeKnownBits/simplifyDemandedBits as a separate patch.

I've added a constructor that allows initializing both APInts to the same bit width with a starting value of 0. This reduces the repeated pattern of initializing both APInts. Once place default constructed the APInts so I added a default constructor for those cases.

Going forward I would like to add more methods that will work on the pairs. For example trunc, zext, and sext occur on both APInts together in several places. We should probably add a clear method that can be used to clear both pieces. Maybe a method to check for conflicting information. A method to return (Zero|One) so we don't write it out everywhere. Maybe a method for (Zero|One).isAllOnesValue() to determine if all bits are known. I'm sure there are many other methods we can come up with.

Differential Revision: https://reviews.llvm.org/D32376

llvm-svn: 301432

1 files changed, 8 insertions, 11 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
index c1eeef646fc..776686d3d11 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombineInternal.h
@@ -489,10 +489,9 @@ public:
     return nullptr; // Don't do anything with FI
   }
 
-  void computeKnownBits(Value *V, APInt &KnownZero, APInt &KnownOne,
+  void computeKnownBits(Value *V, KnownBits &Known,
                         unsigned Depth, Instruction *CxtI) const {
-    return llvm::computeKnownBits(V, KnownZero, KnownOne, DL, Depth, &AC, CxtI,
-                                  &DT);
+    return llvm::computeKnownBits(V, Known, DL, Depth, &AC, CxtI, &DT);
   }
 
   bool MaskedValueIsZero(Value *V, const APInt &Mask, unsigned Depth = 0,
@@ -536,25 +535,23 @@ private:
 
   /// \brief Attempts to replace V with a simpler value based on the demanded
   /// bits.
-  Value *SimplifyDemandedUseBits(Value *V, APInt DemandedMask, APInt &KnownZero,
-                                 APInt &KnownOne, unsigned Depth,
-                                 Instruction *CxtI);
+  Value *SimplifyDemandedUseBits(Value *V, APInt DemandedMask, KnownBits &Known,
+                                 unsigned Depth, Instruction *CxtI);
   bool SimplifyDemandedBits(Instruction *I, unsigned Op,
-                            const APInt &DemandedMask, APInt &KnownZero,
-                            APInt &KnownOne, unsigned Depth = 0);
+                            const APInt &DemandedMask, KnownBits &Known,
+                            unsigned Depth = 0);
   /// Helper routine of SimplifyDemandedUseBits. It computes KnownZero/KnownOne
   /// bits. It also tries to handle simplifications that can be done based on
   /// DemandedMask, but without modifying the Instruction.
   Value *SimplifyMultipleUseDemandedBits(Instruction *I,
                                          const APInt &DemandedMask,
-                                         APInt &KnownZero, APInt &KnownOne,
+                                         KnownBits &Known,
                                          unsigned Depth, Instruction *CxtI);
   /// Helper routine of SimplifyDemandedUseBits. It tries to simplify demanded
   /// bit for "r1 = shr x, c1; r2 = shl r1, c2" instruction sequence.
   Value *simplifyShrShlDemandedBits(
       Instruction *Shr, const APInt &ShrOp1, Instruction *Shl,
-      const APInt &ShlOp1, const APInt &DemandedMask, APInt &KnownZero,
-      APInt &KnownOne);
+      const APInt &ShlOp1, const APInt &DemandedMask, KnownBits &Known);
 
   /// \brief Tries to simplify operands to an integer instruction based on its
   /// demanded bits.